The present inventions relate generally to mechanisms for controlling the interface between an optical fiber and a photonic device in an optoelectronic package. More particularly, a tapered dam structure that defines the relative positioning between the photonic device and the optical fiber(s) and is described. The dam structure may also be used to help contain a clear molding material that seals and protects the photonic device.
Optical networks have a wide variety of applications and are, for example, widely used within the telecommunications, data transmission and high speed networking industries. The optical devices used to convert electrical signals into light signals and light signals into electrical signals are key components in any such optical network. Generally, such devices include one or more photonic elements (e.g. detectors and/or laser emitters) together with the electronic circuitry necessary to drive the photonic elements (e.g., receiver, transmitter or transceiver circuitry). Although a wide variety of optical transceiver devices are currently commercially available, there are always continuing efforts to improve their design and functionality as well as to lower their production costs.
At the time of this writing, most commercially available photonic devices are placed in sealed packages such as TO (transistor outline) metal cans or ceramic chip carriers. A transparent glass or plastic window is then positioned over the active area of the photonic device. The die is typically adhered to the carrier and electrically connected to traces on the carrier using wire bonding.
One issue that is fundamental to the design of any photonic device is the desire to (relatively) efficiently optically couple each active facet (i.e., emitter or detector) of the photonic device to its associated optical fiber. The coupled power on launch (lasing) must be enough to supply the complete link but not so high that laser safety is compromised. When photonic devices are packaged in metal cans or ceramic carriers, there is an inherent standoff distance between the optical fiber or fiber bundle and the active facets of the devices. Typical standoff distances in currently available packages tend to be in the range of 1-5 mm depending upon the type of packaged used. At these distances, it becomes important to collimate the optical fibers to insure good optical coupling between the fibers and the photonic elements. Typically collimation is accomplished by providing a simple lens at the termination of the optical fiber.
One approach to maintaining a close coupling between the photonic device and the optical fiber is to control the standoff distance between the two components. This can be done, by placing a spacer on the base that supports the photonic device. Although the use of a spacer has significant appeal (and indeed the approach can be used with success), there are some practical drawbacks to this approach. Most notably, it can be difficult to provide precise quality control of the standoff distance. More specifically, when an integrated circuit wafer is fabricated, it will have a designated nominal thickness. However, as a practical matter there tend to be thickness variations between different photonic wafers, which results in thickness variations in their respective dice. One cause for the thickness variations stems from the fact that photonic wafers are typically background to a desired thickness. However, the typical grinding process is accurate only to within about 0.5 mil (13 microns) of the targeted thickness. Thus, different wafers may have different thickness, and mixing dice from these wafers will potentially impact the ability to accurately obtain the desired fiber standoff. Therefore, in a transceiver configuration, detector and laser dice must be pre-measured for thickness pairing. Similarly, when a spacer is fabricated, there are spacer production tolerances as well (although the spacer production tolerances tend to vary less than the wafer thickness). If the die thickness varies too much, there may be production problems using a spacer to provide the desired standoff between the die and optical fiber. For example, if the die is too thin relative to the spacer, then the gap between the fiber and the active facet may be farther than desired which reduces optical coupling. Alternatively, if the die is too thick relative to the spacer, then the gap is too small which may result in mechanical damage during the assembly process. One approach to addressing these tolerance problems is to sort and match the dice and spacers to provide the desired standoff. However, such an approach is less than optimum.
Another well known issue that arises in packaging optoelectronic devices relates to interference caused by back reflection. More specifically, light reflecting back off one of the interface components (e.g., a window, the optical fiber tip, or the photonic device) may interfere with the optical coupling and/or create optical interference. One approach to ameliorating these effects is to chamfer a portion of the distal tip of the optical fiber. This often also involves chamfering a portion of the fiber termination that supports the optical fiber as well. Although such grinding does tend to improve performance, it is an expensive and difficult step in the manufacturing process.
Although the described packaging techniques work well, they are relatively expensive to produce. Accordingly, there are continuing efforts to provide improved optical component packaging techniques that help reduce the size and costs of the optical components.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, an optoelectronic component is described that includes a photonic device carried by a substrate. A support structure having a relatively higher portion and a relatively lower portion is formed on or attached to the substrate. In a preferred embodiment, the support structure is a dam structure formed by dispensing a flowable material onto the substrate and hardening the dispensed material. However, spacer stacks or a variety of other devices may be used to form the support structure in alternative embodiments. The optoelectronic component further includes one or more optical fibers, with each optical fiber being in optical communication with an active facet on the photonic device. The relatively higher and lower portions of the support structure are arranged to position the optical fiber(s) at a desired standoff distance from the photonic device and to slightly incline the distal tip of the optical fiber relative to the top surface of the photonic device.
The described packaging approach can be used in both single fiber and multi-channel devices. In some specific embodiments, the support structure is arranged to engage a fiber termination that holds the optical fiber(s). In other embodiments the support structure directly contacts a cladding portion of the optical fiber.
An optically clear cap may also be provided to cover the active facet of the photonic device. In embodiments where the support structure surrounds the photonic device, the support structure may be used as a containment for the cap. With this arrangement, a flowable clear topping material is dispensed over the photonic device without requiring a traditional molding operation. The cap may be formed from any suitable optically clear material. By way of example, optically clear epoxy works well.
The dam structure may also be formed from a variety of materials. One preferred approach is to dispense and cure an epoxy based material. When desirable, the dam structure may be formed from a plurality of independently dispensed dams.
In some specific embodiments, the substrate takes the form of a flexible material having electrically conductive traces thereon that are electrically connected to the photonic device. In these embodiments, an optical component support block may be provided to support the flex material. In other implementations, the base substrate may be a ceramic form printed with electrically conductive traces. In some implementations, a semiconductor die that drives the photonic device may be directly soldered to the traces on the flexible material.